Alumintjm alloys for galvanic anodes



United States Patent Japan No Drawing. Filed Feb. 27, 1963, Ser. No. 261,519 Claims priority, application Japan, July 18, 1962, 37/ 29,639

1 Claim. (Cl. 75146) This invention relates to aluminum alloys for galvanic anodes of even better performance characteristics obtainable through further improvement of the aluminum alloys for galvanic anodes of the Japanese Patent No. 254,043 (pat. publication No. 2,003/1959) granted to the present applicants.

The aluminum alloys for galvanic anodes principally known at present are the alloy formed by adding 5% of Zinc to aluminum (commonly known as Alcoa aluminum anode), the aluminum alloys of the above-mentioned Japanese Patent No. 254,043 granted the invention of the present applicants, that is, the alloys formed by the addition of a total of 0.1 through percent of indium and or tin to aluminum, and the alloys formed by further adding from 1 through 10 percent of zinc to said aluminum alloys of Patent No. 254,043. In addi tion, such alloys as those formed by adding zinc and mercury, by adding calcium, by adding Zinc and calcium, and by adding zinc and a small quantity of manganese to aluminum are also known as alloys for galvanic anodes.

The anode potential of the alloy formed by adding 5 percent of zinc to aluminum is, in sea water, -0.95 volt (all electrical potentials mentioned in the present specification being values referred to a saturated calomel electrode), and its galvanic current efficiency is a mere 50 to 60 percent. Moreover, the anode potential of each of the alloys formed by adding zinc and mercury to aluminum, adding zinc and calcium to aluminum, and adding zinc and manganese to scrap aluminum is of the order of 0.85 to 0.90 volt, and the anode potential of the alloy formed by adding calcium to aluminum is a mere 0.75 to 0.80 volt. In the case of each of these alloys, the galvanic current efliciency is 50 percent or lower, and none of these alloys has satisfactory performance as a galvanic anode. On the other hand, the aluminum alloy anodes of the afore-mentioned Patent No. 254,043 exhibit anode potentials of 1.0 through 1.25 volts in sea water and galvanic current efiiciencies of 70 through 80 percent in the case of an alloy in which high-purity aluminum as been used and of 50 through 60 percent in the case of an alloy in which auminum of ordinary purity such as 99.7% has been used.

By subsequent research on the aluminum alloy anodes of the afore mentioned Patent No. 254,043, we have discovered that a so-called ternary alloy formed by simu taneously adding indium and zinc to aluminum, with an indium content of less than 0.1 percent, has characteristics which, as those of the galvanic anode, are superior to the characteristics of the aluminum alloy anodes of the said patent. In the case of the said patent, the reason for limiting the minimum quantity of the added indium to 0.1 percent was that, as a result of experimental investigation, it had been found that an alloy formed by adding less than 0.1 percent of indium to aluminum exhibits an anode potential of 1.0 volt or higher, and, moreover, the reproducibility of the anode potential of the said alloy is poor. However, it has subsequently become apparent that, in the case of alloying aluminum with both indium and zinc, the limiting of the quantity of added indium to less than 0.1 percent, on the contrary, produces a product with superior performance.

It is an object of the present invention to utilize the a-bovestated discoveries and thereby provide alloys for galvanic anodes of superior characteristics.

For example, an alloy formed by adding 0.02 percent of indium and 2.5 percent of zinc to aluminum of ordinary purity exhibits an anode potential of the order of 1.1 volts and a galvanic current efficiency which, although varies with conditions of use, attains a value approximately 70 to percent. Further, in the case of a binary alloy produced by adding 0.01 percent of indium to an aluminum material of high purity the anode potential is of the order of 0.75 volt, which is insuflicient to act as a galvanic anode, a ternary alloy produced by the addition of 0.01 percent of indium and 2.5 percent of zinc to the same high-purity aluminum material eX- hibits an anode potential of about 1.1 volt and becomes an excellent galvanic anode.

In the case of a binary alloy consisting of aluminum and a small quantity of indium, segregation is liable to occur during its casting, and the said alloy has a tendency to corrode irregularly during use. It has been found, however, that by simultaneously adding zinc and indium to aluminum, the corrosion pattern of the alloy is remarkably improved.

It must be added that an alloy containing 0.1 percent or more of indium, or an alloy formed by adding zinc simultaneously with the said quantity of induirn, incurs a relatively high rate of self-corrosion when it is used as a galvanic anode, and its galvanic current emoiency does not exceed the range of 50 to 60 percent in the case wherein aluminum material of ordinary purity has been used in its alloying.

The aluminum alloy anode of the present invention containing less than 0.1 percent of indium as described above has a reduced quantity of added indiurn, which is a relatively high-priced metal, and not only aifords, thereby, economy in cost, but also affords improvement of anode characteristics, particularly substantial improvement of galvanic current efliciency, which is highly ad vantageous in practical uses.

In carrying the invention into practice, however, certain limits of additive quantities for alloying have been disclosed. Furthermore, it has been found that the addition of less than 0.005 percent of indium produces an alloy having a performance approaching that of an aluminum-zinc alloy, wherefore almost no advantageous efiect of indium can be discerned. It has been found further that, while zinc added simultaneously with indium produces substantially the same efifect throughout the range of 0.5 through 20 percent and differences in the added quantity of zinc do not impart a great influence on the performance of the alloy, the eitect of the zinc progressively declines with added quantities of zinc below 0.5 percent. With added quantities of zinc above 20 percent, the anode performance is impaired, and such disadvantages as the formation of cracks around the steel insert during casting are likely to be incurred. Accordingly, the aluminum alloy anode of the present invention is characterized by the simultaneous addition of indium of a quantity which is less than 0.1 percent and greater than 0.005 percent and zinc of a quantity in the range from 0.5 through 20 percent, inclusive, to aluminum. It has been found that an aluminum alloy containing approximately 0.02 percent of indium and 2.5 percent of zinc is most suitable as an anode material from considerations of performance and economy.

In order to indicate still more fully the anode characterist-ics of the alloy according to the present invention, an example of results of comparative tests on the galvanic characteristics of the aluminum alloy of this invention and of the aluminum alloy of the aforementioned Patent No. 254,043 is presented in the accompanying Table 1.

Table 1 As indicated in Table 1, the aluminum alloy anodes [Anode potentials and galvanic current efficiencies (in the case ofgahmn f thi i ti (s k 1 h h 7) hibit a k d improvement action in synthetic sea Water at an anodie current density of 1.5 ma./cm.

indium;

f 1 o m g H .m m t .S u n H mm 0 e c m w a e .1 w P e .m m m w m s l C mu n E T n .V a v N 6 .w m e E .m n 5 b m T a 0 6 A V O h V. a g C d .n e N V. r. n n 0 1M .1 H G .a W 6 S E J O r B e R i .B O C m 0 P d 9 F 9 e d P u 5 K m H m r. 4 c v w m a m. E m d m i R E S 0 W 3 .1 .1 u 4 C t 1 m 0 nu D fi a a 2 l 1 h h 4 I 6 W H T m H .V t m A us 5. A r hi0 D O 5 5 1 1 34802450005000 0 y) 8977887655567 .lwr c nn mmm mmma GCEW mmfrm wm fl www m%%mwm%n m w m+ w LLLLLLLQLLLQO emm wmo mfi a /W PA G W .0 m "m .S6 H5 0 Z0 PM 0 mp mm u :1 1 m m .i m w MW 00000000001 LLLLLLLLLLLLM AAAAAAAAAAAA OWQMQWOWQWQQQOWQWOWOWI 999999999999 l p m S NOTE: 20

(l) G) designates alloys of this invention.

(2) Valuesof galvanic current efficiency are calculated with electrochemical dissolution of Zn taken into account.

Notice of Adverse Decision in Interference In Interference No. 95,327 involving Patent No. 3,172,760, T. Salmno and K. Toda, ALUMINUM ALLOYS FOR GALVANIO ANODES, final judgment adverse to the patentees Was rendered J an. 30, 1968, as to claim 1.

[Ofiioz'al Gazette July 2, 1968.] 

